Communications standards are developed in order to provide global connectivity for wireless systems and to achieve performance goals in terms of, for example, throughput, latency and coverage. One current standard in widespread use, called high speed packed access (HSPA), was developed as part of Third Generation (3G) Radio Systems, and is maintained by the Third Generation Partnership Project (3GPP).
High-Speed Packet Access (HSPA) is a collection of mobile telephony protocols that extend and improve the performance of existing Universal Mobile Telecommunications System (UMTS) protocols. High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) provide increased performance by using improved modulation schemes and by refining the protocols by which handsets and base stations communicate.
HSPA provides improved theoretical downlink (DL) performance of up to 14.4 Mbit/s and improved theoretical uplink (UL) performance of up to 5.76 Mbit/s. Existing deployments provide up to 7.2 Mbit/s in the DL and up to 384 kbit/s in the UL. Evolved HSPA is defined in 3GPP Release 7. It introduces simpler architecture for the mobile network by bypassing most of the legacy equipment and enhancing radio data rates.
Above the physical layer in a 3GPP system, a Medium Access Control (MAC) layer may be divided into several entities. A new MAC entity, MAC enhanced high speed (MAC-ehs), has been introduced and optimized for HSPA in the DL. The MAC-ehs entity can be used alternatively to MAC high speed (MAC-hs). In the UL a new MAC entity, improved MAC (MAC-i/is) has been introduced and optimized for HSPA. The MAC-i/is entity can be used alternatively to MAC-e/es. The MAC-ehs and/or MAC-i/is entity is configured by higher layers which are configured to handle the data transmitted on the High Speed Downlink Shared Channel (HS-DSCH) and/or Enhanced Uplink Channel (E-DCH) and manage the physical resources allocated to HS-DSCH.
The MAC-ehs entity allows the support of flexible radio link control (RLC) protocol data unit (PDU) sizes as well as MAC segmentation and reassembly. Unlike MAC-hs for HSDPA, MAC-ehs allows the multiplexing of data from several priority queues within one transmission time interval (TTI) of 2 ms.
The scheduling/priority handling function is responsible for the scheduling decisions. For each TTI of 2 ms, it is decided whether single or dual stream transmission is used. New transmissions or retransmissions are sent according to the acknowlegdement/negative acknowledgement (ACK/NACK) UL feedback, and new transmissions can be initiated at any time. While in the CELL_FACH, CELL_PCH, and URA_PCH states, the MAC-ehs can additionally perform retransmissions on HS-DSCH without relying on uplink signaling.
Reordering on the receiver side is based on priority queues. Transmission sequence numbers (TSN) are assigned within each reordering queue to enable reordering. On the receiver side, the MAC-ehs SDU, or segment thereof, is assigned to the correct priority queue based on the logical channel identifier.
The MAC-ehs SDUs can be segmented on the transmitter side and are reassembled on the receiver side. At the MAC layer, a set of logical channels is mapped to a transport channel. Two types of transport channels include, a “common” transport channel (MAC-c) which can be shared by multiple WTRUs, and a “dedicated” transport channel (MAC-d) which is allocated to a single WTRU. A MAC-ehs SDU is either a MAC-c PDU or MAC-d PDU. The MAC-ehs SDUs included in a MAC-ehs PDU can have different sizes and different priorities and can belong to different MAC-d or MAC-c flows.
The typical baseline of the MAC-ehs header results in fairly low overhead when the MAC-ehs multiplexes logical channels that are used by Release 7 RLC acknowledge mode (AM) instances configured with a flexible RLC PDU size. This is due to the size of a MAC SDU being significantly larger than the total size of the different fields of the header.
However, there are situations where the typical baseline would result in an undesirable level of overhead. For example, a logical channel is used by an RLC AM instance configured with a fixed RLC PDU size, or to a Release 6 RLC AM instance. The latter instance may result from the possibility of enabling handover from a Release 6 base station to a 3GPP Release 7 base station without resetting the RLC and keeping the RLC entity configured to operate with fixed RLC PDUs. In another example, the MAC-ehs PDU size possible with current channel conditions is small and contains a few (e.g., 2) segments of SDUs. In this example, the header may constitute a significant overhead.
Typical signaling requirements to support MAC-ehs functionalities are inefficient. It would be desirable to reduce the amount of signaling required to support MAC-ehs PDU functionalities. One possibility to reduce signaling would be to perform multiplexing/de-multiplexing of SDUs of different sizes, from different logical channels and priority queues in a single MAC-ehs PDU at the base station. Another possibility would be to perform multiplexing/de-multiplexing of SDUs of different sizes and belonging to different logical channels. Finally, concatenation/disassembly and segmentation/reassembly of MAC-ehs SDUs would be desirable.
Table 1 shows encoding of the segmentation indication (SI) field, when the segmentation indication is defined per priority queue. The meaning of the field may cause confusion at the WTRU side when padding is present at the end of the MAC-ehs header after the last segment of an SDU. In this case, the segmentation indication as per the indicated encoding would need to be “11.” However, the WTRU could interpret this as meaning that the SDU is not complete and insert it in a reassembly buffer. It would be desirable to modify the encoding of this field to avoid this confusion.
TABLE 1SI FieldSegmentation indication00The first MAC-hs SDU of the addressed set ofMAC-hs SDUs is a complete MAC-d PDU.The last MAC-hs SDU of the addressed set ofMAC-hs SDUs is a complete MAC-d PDU.01The first MAC-hs SDU of the addressed set ofMAC-hs SDUs is a segment of a MAC-d PDU.The last MAC-hs SDU of the addressed set ofMAC-hs SDUs is a complete MAC-d PDU.10The first MAC-hs SDU of the addressed set ofMAC-hs SDUs is a complete MAC-d PDU.The last MAC-hs SDU of the addressed set ofMAC-hs SDUs is a segment of a MAC-d PDU.11The first MAC-hs SDU of the addressed set ofMAC-hs SDUs is a segment of a MAC-d PDU.The last MAC-hs SDU of the addressed set ofMAC-hs SDUs is a segment of a MAC-d PDU.